1. Field of the Invention
The present invention relates to an exhaust circulation control valve for automotive engines where the amount of exhaust gas recirculated in the inlet system of an engine is controlled. More specifically, the present invention relates to an exhaust gas circulation control valve having an exhaust gas inlet port for letting in exhaust gas and an exhaust gas feed port for introducing the exhaust gas into the inlet system. An aperture is formed to make the ports continuous. The opening and closing of the aperture is controlled by the lift of the valve.
2. Description of the Related Art
In automotive engines, exhaust gas recirculation (EGR) is used to reduce the emission of nitrogen oxides. A portion of the exhaust gas generated in the combustion chamber is returned to the inlet system and added to newly introduced air. With this type of EGR system, circulation of exhaust gas that is excessive with regard to the state of the engine can result in unstable combustion and a significant decrease in engine output. If circulation is inadequate, it is not possible to take full advantage of EGR. Thus, in order to use EGR efficiently and provide optimum emission characteristics and fuel consumption, it is necessary to control the amount of recirculated exhaust gas in a manner corresponding to the engine state. This type of control is generally performed via an exhaust gas circulation control valve disposed in an exhaust gas circulation path connecting the exhaust system and the inlet system of an engine. In this type of exhaust gas circulation control valve, an exhaust gas inlet port connected to the exhaust gas path of the engine and an exhaust gas feed port connected to the inlet path of an engine are made continuous via an opening disposed between the two ports. The area of the opening is made variable via the lift of the valve.
In order to provide appropriate control over a wide range of engine states, an exhaust gas circulation control valve must have flow control properties that vary according to the operating state of the engine. For example, when an automobile is running normally, a small amount of exhaust gas must be controlled and circulated with a high degree of precision. On the other hand, a large amount of exhaust gas should be circulated during acceleration, so the exhaust gas circulation control valve must be responsive to large flows as well.
In order to fulfill these requirements, Japanese Examined Patent Publication Number 56-30681 proposes a structure wherein an exhaust gas inlet port and an exhaust gas feed port are made continuous via two openings disposed between the two ports. Valves for each of these openings are opened and closed separately. These valves are driven by separate drive mechanisms.
With this type of exhaust gas circulation valve, large amounts of exhaust gas can be circulated (e.g., during acceleration of the automobile) by opening both openings. Also, when high engine output is required (e.g., when going up a hill), a small amount of exhaust gas can be controlled and circulated with a high degree of precision by closing one of the valves. Thus, the exhaust gas circulation control valve can handle different flow control properties.
However, with the exhaust gas control valve described above, two valves must be driven by separate external drive mechanisms. This makes the overall valve system, including the drive mechanisms, large and complex. Also, the margin of error generated by each drive mechanism makes maintaining a high degree of precision difficult.
Furthermore, with exhaust gas circulation control valves, the adhesion of carbon to the valves is a problem, and the structure described above does not address this problem.